HASTINGS, APRIL 14, 2007

by   Linda Hamling

We met Ken Brooks of the Hastings Geological Society at the Smugglers Pub (TQ 890133) at Cliff End on the Sussex coast near Fairlight east of Hastings, where we were joined by several readers of “Down To Earth”. Together we marvelled at some impressive local fossils, which Ken produced from the boot of his car and had found in the coastal exposures. Out of the Ashdown Sandstone and Wadhurst Clay, 130-125 Ma old, he showed us fish scales of Lepidotes mantella, gastropods (Viviparus) and bivalves (Neomiodon), turtle scutes, an Iguanodon tooth, crocodile teeth and the large fin spine of the shark Hybodus ensis. We were also shown casts of the footprints of an Iguanodon and of a Theropod out of the Fairlight Clays, 130-135 Ma old.

 We then set out westwards along the seawall to see the cliff section. At the lowest extent of the tidal range a submerged forest is exposed, containing wood and other remains of hazel, birch and beech dating from 3000 BC. The sea level at the time must have been lower to allow these trees to grow. However, we weren’t to see it as the tide was then too high. The beginning of the cliff section is cut in Wadhurst beds, the Cliff End Sandstone with shales above. Two normal faults, the Cliff End Faults, dislocate the bedding and have led to folding of the shales above. They resulted from tension during the uplift of the Weald. The sandstone is composed of flood plain deposits and the shales were laid down under subsequent quiet water conditions. The shales are dark in colour because of carbon from plants, which had colonised them. A cave had been eroded by meltwater from permafrost at the end of the last (Devensian) cold stage of the Pleistocene. Inside Mesolithic scrapers had been found. At the top of the cliff, we could see the base of the Ashdown Formation, which contains charcoal from forest fires at the time of deposition.

 Lying loose on the beach were blocks of the Cliff End Bone Bed, a coarse fossiliferous sandstone containing numerous nodules of sideritic ironstone, small teeth of the fish Lepidotes and pieces of bone. This was probably a flash flood deposit from which the finer components had been washed downstream. Other blocks from the Wadhurst beds displayed bioturbation, probably bivalve pellets, bivalves and plant material in the form of charcoal swept into the deposit. Gutter casts, tiny water channels trending in one direction, had been cut into the rock surface. The sandstone was stained in varying shades of red by iron in its differing states of oxidation. Siderite is brown, limonite is yellow and haematite red. The instability of the cliff was well illustrated by a sudden collapse of part of the face, which startled us. Ken repeatedly emphasized the importance of staying well away from the base of the cliff.

 We came upon “walls” in the beach, which for all the world looked like the foundations of buildings. However, Ken explained that they had been formed by deposition of iron percolating down through cracks and thus hardening the adjacent sandstone. The rest of the sandstone had been eroded away to leave these impressive ‘pseudo-rooms’. A beach boulder had numerous stems of the horsetail Equisetites in it. We also saw disturbance of the sediment resulting from three-toed footprints of Iguanodon or a theropod dinosaur (‘dinoturbation’).

Fig. 1  Channel in the Ashdown Sandstone exposed on the shore near Haddock’s Cottages.

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 Further west, the cliff intersects a reversed fault known as the Haddock’s Fault. The younger Wadhurst beds exposed to the east were brought into contact with the Ashdown Sandstone Formation to the west, with sandstones overlying the Fairlight Clay. On the shore a channel in the Ashdown Sandstone cutting across earlier strata was well exposed (Fig. 1). West of the fault the cliff is subject to frequent landslips, which endanger Haddock’s Cottages on the cliff top and have necessitated the use of large larvikite blocks to prevent waves attacking the base of the cliff (Fig. 2). We took advantage of the larvikite blocks to eat our lunch. Because of the beach protection, the cliff has become sufficiently stable for vegetation to develop on it, but elsewhere the lack of vegetation indicated continuing instability.

Fig. 2  Blocks of larvikite used for sea defence to protect the cliff cut in Ashdown Sandstone at Haddock’s Cottages, near Fairlight.

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 As at the “White Rock” in Hastings, salt encrustation has whitened the sandstone cliffs near Haddock’s Cottages. Another channel exposed in the cliff could be the cross section of a meander bend because it was asymmetrical with more sediment on one side, which would be the inside of the bend.

 After lunch, we walked westwards as far as the Fairlight Reverse Fault, which brings a much greater thickness of Fairlight Clay into the Cliff, but then had to turn back. This had been a lovely walk on a day, which was hot though cooled by pleasant onshore breezes. Our thanks to Ken Brooks for leading us and explaining the interesting geological features of this very impressive stretch of coast.

PEAK DISTRICT, MAY 18-20, 2007

by   Linda Hamling

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SATURDAY

The Ashover Anticline has much landscape value as well as being of geological interest, having been described as the Peak District in miniature. We were able to appreciate this from the viewpoint of Fabrick Point, a hill of Namurian Ashover Grit to the north-west of Ashover, to which our leader Ian Sutton had taken us. Looking east, we had a panoramic view of the Derbyshire coalfield and its associated old mining villages on the Upper Carboniferous, with the Permian Magnesian Limestone forming the higher ground on the horizon. The Millstone Grit on which we were standing dips under the coalfield to the east. The vegetation on the gritstone, with heather, bilberry and coarse grasses, reflects the typical acid soils.

 To the west we looked over a charming vale, sited over the Ashover Anticline. Although the whole area was covered by ice about 450,000 years ago in the Anglian Glaciation, it was not glaciated in the last (Devensian) glaciation. Consequently glacial deposits are very patchy in the Peak District, and the landscape strongly reflects the bedrock structure and lithology. The Edale Shales beneath the Ashover Grit form the floor of the Ashover Valley. On the western side of the valley the gritstone escarpment was considerably steeper than where we were standing on the east side. On Fabrick Point we were on almost a hogsback. In the foreground below us the shales formed low ground, beyond which a low rise indicated the outcrop of the Carboniferous Limestone in the core of the anticline. Hidden from view by trees was the River Amber flowing over volcanic rocks underlying the limestone. Beyond this, the land again rose over the limestone outcrop before descending because onto the softer shales, only to climb steeply up the gritstone escarpment. The lead-mining village of Ashover stands on the limestone because the lead was initially extracted from the limestone.

 We examined the gritstone. To the north there was high ground in the Namurian, which was being eroded by rivers that contributed to the formation of a delta that progressively migrated southwards. It had reached the Peak District by the Upper Carboniferous. The high ground comprised schists, gneisses and granites and minerals derived from of all of these could be seen in the grits. The presence of muscovite mica has contributed to bedding, making the gritstones suitable as flagstones. Britain was close to the Equator at this time and tropical conditions pertained. Flash flooding led to thick individual gritstone units, which are considered to be the product of single floods. Fossil trees have been found buried upright in the deposits of the floods. Earlier in the Carboniferous there were quiet conditions of sedimentation, during which the shales were laid down beyond the advancing delta front.

 Leaving the windy top we parked in Ashover to walk across the limestone on which Ashover is built to see the underlying volcanics. Our stay coincided with wonderful spring flowers, and on this walk we saw, amongst others, Yellow Archangel, Broomrape (symbiotic on Beech), Ransoms, Speedwell, Vetch, Bluebells, Red Campion, Herb Robert and Garlic Mustard. In the boulders of limestone incorporated into the field walls, we saw fluorspar, calcite and crinoids. The limestone is bioclastic, high energy water having broken up the shells. Some fossils have been replaced by silica making them resistant, so that they stood proud from the fine limestone matrix. Chert of uncertain origin was also present. The tips remaining after lead mining subsequently became an important source of fluorite, and so had disappeared from the fields. We climbed up the limestone rise to then descend onto the shales. At the junction of the gritstone and the impermeable shales are springs, and the ground beneath was very damp as a result. Grooves had been eroded in the paving stones of the path by traffic from the mine, Robin Quarry, which we were entering. The mines here were especially active in the 18th and 19th centuries. A chimney was testament to smelting activities. A hill not far off stood free from the main escarpment having been offset by a fault. As swallows swooped overhead we searched the waste for minerals. Fluorite, calcite, baryte, galena, sphalerite and arsenopyrite were found. We smelt the arsenopyrite when it was freshly exposed as it characteristically gives off a smell of garlic. On our return we saw Wood Sorrel and Meadow Saxifrage, which is an indicator of limestone. We also stopped to examine the volcanic rocks. Sixty metres of basaltic tuff had been laid down, probably having been erupted into water, but the location of the volcano is unknown. It was fairly well bedded and in places quite coarse, and had a greenish appearance due to the presence of chlorite, a weathering product. The rock has been quarried for gritting roads in icy conditions. The tuff in known to be underlain by further limestones, so it forms part of the Carboniferous Limestone succession. Where two lava flows cross the Via Gellia in the Peak District there are springs owing to the impermeability of the lava, and here the water is laden with calcium carbonate resulting to the formation of tufa. ndeed a cottage in the Via is built mainly of tufa.

 Back in Ashover we enjoyed a lovely lunch at the Crispin Inn, so named as soldiers returned there after the Battle of Agincourt. A sharp shower caught us out as we returned to our cars but a wise little kitten remained bone dry by sheltering in a bush before greeting us after the rain stopped.

 In the afternoon, we went on to explore Fall Hill Quarry. This was another haven for flowers including Valerian, Cowslips, Wild Forget-Me-Not, Vetch, Hawkweed, Red Campion, Buddleia and Speedwell. The quarry face ran along a fault line along which mineralisation had occurred. Slickensides were to be seen. The fault was expressed as a notch in the quarry face on the far side (Fig. 3). A house had been built over it and so the depression had been infilled with gabions to stabilize it. On one side of the fault was volcanic ash, which had been upthrown against to the limestone. The movement had dragged down the beds of limestone against the fault. The fault line had enabled the passage of fluids leading to mineralisation. Fluorite was most commonly found mineral, and we saw cubic crystals 2-3 cm across in blocks of the limestone. Quartz and galena were also collected.

In the afternoon, we went on to explore Fall Hill Quarry. This was another haven for flowers including Valerian, Cowslips, Wild Forget-Me-Not, Vetch, Hawkweed, Red Campion, Buddleia and Speedwell. The quarry face ran along a fault line along which mineralisation had occurred. Slickensides were to be seen. The fault was expressed as a notch in the quarry face on the far side (Fig. 3). A house had been built over it and so the depression had been infilled with gabions to stabilize it. On one side of the fault was volcanic ash, which had been upthrown against to the limestone. The movement had dragged down the beds of limestone against the fault. The fault line had enabled the passage of fluids leading to mineralisation. Fluorite was most commonly found mineral, and we saw cubic crystals 2-3 cm across in blocks of the limestone. Quartz and galena were also collected.

Unfortunately there was a public event taking place in Butts Quarry, so we were unable to explore it. Nonetheless at the entrance the volcanic ash was well exposed. It was well bedded with coarse material at the bottom fining upwards. The copper carbonate, malachite, was found in this lapilli tuff.

 We then enjoyed tea at Lea Gardens, a paradise of rhodedendrons, before going on to the National Stone Centre near Wirksworth. First, we walked along the High Peak Trail to Steeplehouse Quarry, which is in the Cawdor Limestones, at the very top of the Carboniferous Limestone in Derbyshire. The dip here is very gentle. This quarry is famous for the innumerable shark dermal denticles, which can be collected from the limestone. Near the information centre is a display of drystone walling from many parts of Britain (Fig. 5), and we walked the walls to see the designs and materials used. In Coleshill quarry, below well bedded limestone, we saw a massive reef structure formed from coral and bryozoans together with brachiopods including Gigantoproductids.

SUNDAY

On Sunday we drove to leave two cars in Hartington, so that we might return from a linear walk between our hotel in Biggin and the village of Hartington. Along with other walkers, we began our walk down Biggin Dale (Fig. 6). The Beelow Limestone, through which this valley is cut, dip very gently W-E. It is a tributary valley of the Dove, cut in cold periods of the Quaternary by rapid water flows from spring melting of snow and ice. Nowadays its water table height is similar to that of the Dove, so it is a dry valley. Again wild flowers such as Cuckoo Flower, Meadow Saxifrage, Cowslips, Early Purple Orchid and Ladies Bedstraw were everywhere. It was interesting to see a sewage plant with a cleansing reed bed. There was no associated smell at all! As we passed by fields of sheep on our descent, we were astonished to see the sheep respond to being called by their owners and running up to them. The owners’ sheepdogs were rendered redundant! There was a dew pond in the field and terracettes on the hillsides where there had been mass movement (creep) downhill. Some of the more resistant beds of limestone stood proud from the hillsides.

Soon we turned into Wolfscote Dale, which is cut into the Woo Dale Limestone. At tributary junctions like this, occasional floods have created alluvial fans. During the Pleistocene much bare rock was exposed and freeze thaw action led to formation of the screes, which now litter the hillsides. Vegetation has masked the older screes but the more recent screes are still visible. Weirs impeded the flow of the river creating more favourable conditions for fishermen. We looked in vain for Dippers. Towards the end of Wolfscote Dale are caves in the limestone crags. The valley then opened out into a wide expanse, a flood plain which was boggy underfoot. We had crossed onto the outcrop of impermeable Namurian Shales, which the River Dove had not exploited in its passage south. Instead it had continued to cut down through the harder limestone. Superimposed drainage has been suggested as the reason for this. Butterbur and Water Avens grew alongside the river. The valley narrowed again and we walked through a little gorge where a pillar of limestone rose out of the river bed. The river here was cutting through reef limestone. Its greater resistance had led to the narrowness and the presence of joints had left the pillar stranded by erosion. We then entered another wide part of the valley, which afforded us a viewpoint from where we see the Namurian gritstones dipping to the west. At the reef structure of Penny Low we were able to see the junction between the shales and the limestone. Crinoids were found here.  

 We lunched in Hartington and picked up our cars from there and Biggin before driving to Apes Tor in the Manifold Valley. This is on the western margin of the Carboniferous Limestone in the Peak District. At the end of the Carboniferous there were earth movements in the Variscan Orogeny leading to E-W compression, which generally led to gentle folding. However, here on the western margin of the limestone, the movement was pushing against a resistant stable limestone block, which resulted in more intense folding. The folds are clearly visible from the narrow road through the Manifold Valley. The distorted strata are interbedded limestones and shales laid down in slightly deeper water just off the block. There are also many diatomaceous chert beds, which may be replacement features arising from hydrothermal fluids that were also responsible for local mineralization. The nearby Ecton Hill was the centre of extensive copper extraction in the past. We searched a roadside dump for minerals and found the copper silicate chryscolla and the carbonate malachite. We then briefly examined a quarry where 70-80 years ago scree had collapsed and had subsequently become cemented by calcite from water flowing from the limestone. There were many Orange Tip butterflies but sadly we were too early to harvest the strawberries, which were growing in abundance. Further along was a mine adit in the Ecton Limestones. They comprise bedded limestones, shales and occasional thicker limestones, which are a basin facies right on the western edge of the limestone. As a result, the fossil assemblage is different from other parts of the limestone, consisting mainly of surface dwelling animals. One of the thicker beds had been used as the roof for the adit, which probably dates from the late 18th century and, at 400 feet deep, was at the time the deepest mine in Europe.  

 After a really interesting time in the Peak we took our leave of Ian, thanking him for a lovely weekend. Our thanks to John too for organising the trip and finding such a nice hotel in Biggin-by-Hartington.  

CHAFFORD GORGES NATURE PARK, NOVEMBER 10, 2007

by   John Catt

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After a short drive from Hertfordshire, we meet our leader, Di Clements from the Natural History Museum in South Kensington, at the smart new visitor centre, where we began the day enjoying a coffee looking out over part of the nature park. The Chafford Gorges Nature Park in Essex is within Chafford Hundred, a suburb of Grays on the north bank of the Thames close to the M25 Dartford River Crossing. It comprises three very large chalk quarries, which have been abandoned after many years of chalk extraction for the cement industry. The quarries are now flooded to the level of the local groundwater table in the Chalk, so that they can be used for angling. The sides are attractively wooded, but also provide good exposures of Upper Chalk (mainly Micraster coranguinum zone) and overlying Thanet Beds and Thames terrace gravels. A further Chalk quarry contains numerous circular oil storage tanks, and many areas within and around the quarries have been developed for commuter housing.

 Standing on the terrace in front of the visitor centre, and with a magnificent view across one of the flooded chalk quarries (Warren Gorge) rimmed by woodland and new houses, Di explained that the Chalk in the Grays area occurs at a higher level than elsewhere in south-east London because it lies on the axis of an elongated anticline or pericline of Alpine (mid-Tertiary) age, the Purfleet Anticline. Beneath the gently folded Chalk, the Lower Cretaceous Gault Clay rests unconformably at no great depth on Palaeozoic rocks forming the London-Brabant Massif, which was an area of land or very shallow sea with little or no deposition throughout the Carboniferous Period and for much of Mesozoic time up to the Albian (Gault Clay) marine transgression

 We then walked a short distance into Merlin Close to see some magnificent periglacial involutions formed in a thin layer of Thanet Beds over frost-disturbed Upper Chalk (Coombe Deposit). Di explained that these had formed probably towards the end of the last (Devensian) cold stage of the Pleistocene, between approximately 20,000 to 11,500 years ago. They are indicative of saturated ground conditions during warm summer periods, when the upper 1-2 metres of the ground had thawed above an impermeable layer of permafrost in the Chalk. They seem to occur only where the Thanet Beds cover is fairly thin, providing a strong colour contrast between the yellowish-brown sand and white Coombe Deposit. Where the Thanet Sands are thicker, any structures formed entirely within the sand would be less clearly seen. However, it is possible that they never formed to any extent within uniform sand, as their development may have required a contrast in water content and density between the sand and the Coombe Deposit. The involutions are flask-shaped bodies of sand protruding downwards into the Coombe Deposit. Some have broad, some narrow, necks and others form isolated pockets within the Coombe Deposit, probably where the original connecting neck has been stretched and broken through within the Coombe Deposit. Where the ground surface sloped slightly more steeply (1-2o), the upper part of each involution was inclined down the slope, probably because of downslope mass movement (gelifluction) after their formation.

 We then walked southwards into Devonshire Road, which afforded a clear view of the face of Wouldham Cliff at the edge of the large quarry containing the oil storage tanks. A prominent feature of the Chalk exposed here is the flint band known as Whitaker’s 3-inch band. This is a useful marker horizon within the Upper Chalk throughout south-east England and even further afield. It gave rise to a lengthy but rather inconclusive discussion about the origin of flint bands. The Chalk also contained several accumulations of chocolate-coloured clay in the fissure network several metres below the base of the overlying Thanet Beds. The clay had probably been slowly deposited from water percolating down the fissures from soils on the Thanet Sands.

 The Chalk at Wouldham Cliff was too distant to examine closely, as it is separated from Devonshire Road by a high fence, but at the entrance to the nearby Lion Gorge Chalk Pit we were at last able to get our fingers dirty looking at other flints dispersed through the Chalk and for fossils within the Chalk. The main fossil remains found were fragments of the thick-shelled bivalve Inoceramus, but our efforts were frustrated by a thin layer of mud obscuring much of the chalk surface, which had probably been washed down by the frequent heavy rain earlier in the summer.

 We then walked through Lion Gorge and climbed up to a viewpoint beside Philip Sidney Road, looking southwards along the now abandoned Lion Pit Tramway Cutting towards the River Thames and north Kent on the far bank. The tramway had been cut for a mineral railway carrying chalk from the Lion Gorge Pit to riverside cement works. Di explained that the tramway cutting had exposed a gravel terrace of the Thames containing mammal remains (bones and teeth) of mammoth, horse and northern vole, which the work of Danielle Schreve had shown to be characteristic of the Taplow/Mucking Gravel dated to Marine Isotope Stage (MIS) 7 of the Quaternary. This is equivalent to the penultimate interglacial, which is older than the Ipswichian (MIS 5e) deposits containing a different mammal assemblage (hippopotamus, fallow deer, elephant, rhinoceros) occurring in at a lower level in the Thames Valley at Trafalgar Square in central London. The tramway cutting also yielded human flint artifacts of Levallois type, which first appear in the Thames sequence in MIS 8 or 9, but are absent from the Ipswichian deposits. From examination of the fossil assemblages of deposits of MIS 5e age thoughout Britain, it seems that neither man nor horse was present in Britain at this time, even though both had been common in MIS 7 and some earlier periods.

 Returning through the Lion Pit to Devonshire Road, we examined a section through the unconformity between the Cretaceous and Palaeocene (the local K/T boundary) exposed in The Ramp, a sloping footpath leading up the side of Wouldham Cliff. Near the top of the ramp, the base of the Thanet Beds is almost flat and marked by a thin layer of green-coated flints resting on an eroded surface of Upper Chalk. However, lower down the slope the basal Thanet Beds has been let down into large solution hollows (pipes) in the Chalk below the usual height of the unconformity. The pipes were lined with chocolate-coloured clay containing some green-coated flints but also some fresh flints released from the adjacent chalk. This section is conserved by the Essex Wildlife Trust. At the top of the slope, gravels of an earlier Thames Terrace occur, but the section could not be inspected, as it was behind a high fence and had become overgrown during the summer. These gravels have been correlated with the Boyn Hill Terrace, which contains another mammalian assemblage, including cave bear, large fallow deer, mole, giant beaver and rabbit. This is dated to MIS 11, and equivalent deposits at Hornchurch overlie Chalky Boulder Clay of the Anglian Glaciation (MIS 12). At Swanscombe, across the Thames Valley in north Kent, the same terrace deposits contain Acheulian handaxes and Clactonian chopper tools, and have yielded fragments of a human skull (Swanscombe Man). Boyn Hill Gravels also overlie the Thanet Beds at the viewpoint over Grays Gorge, which we passed on our return to the visitor centre.

 Some of us then had lunch at the visitor centre, while others drove to a pub called the Sandmartin, which seemed to be the only pub in Chafford Hundred. The name proved appropriate because it was situated close to an exposure of the Thanet Beds sand full of sandmartin holes. Di had received a key to a gate in the fence that would have allowed us to examine the sand at close quarters, but it didn’t fit the new lock attached to the gate, so we were only able to view the section from outside the gate. She explained that the Thanet Sand at this site is even finer and more uniform than elsewhere. As a result, it stands in a stable vertical face over 10 metres high, with a very small talus slope at the foot. Very few fossils have been found here, probably because the sand has been decalcified. It also lacks any clear bedding, suggesting that bioturbation soon after deposition or the decalcification have disturbed the deposit throughout.

 Across the main road we were able to open another gate that allowed access to the woodland above Grays Gorge, on the opposite side to that viewed earlier before lunch. Here the main feature seen was a group of sarsen stones, which had probably been excavated from nearby Boyn Hill Gravels overlying the Thanet Beds. The stones were 2-3 metres across and 30-50 cm thick, and Di explained that they had formed by silicification of sand, probably in the Upnor Formation, a Palaeocene marine deposit slightly younger than the Thanet Beds. During the late Palaeocene and early Eocene there had been a sequence of at least five marine transgressions across south-east England, with brief periods of uplift and erosion between. Some had reached further than others, the Upnor trangression reaching further west (across Hertfordshire) than the Thanet transgression, which reached only into the extreme eastern part of Hertfordshire. The subsequent Woolwich transgression reached only into central London, but at the same time the non-marine Reading Beds were deposited further west by rivers flowing into a delta at the edge of the land mass. The later Harwich Formation (= London Clay Basement Bed) and London Clay Formation were deposited following transgressions that again covered Hertfordshire and probably areas further west.

 A particularly interesting feature of all the sarsen stones was their mounded or mammillated upper and lower surfaces. These are typical of most sarsen stones in southern England, and may have formed by growth and eventual amalgamation of a series of originally separate lenticular concretions. There was considerable discussion of the environment in which sarsens and puddingstones might have been formed. Most agreed that a hot, moist tropical climate with rapidly weathering soils was necessary to mobilize the silica and allow its redeposition lower in the soil profile or at slightly greater depth in the earth’s crust within the voids between sand grains (sarsen) or sand containing flint pebbles (puddingstone). As the silica-enriched waters could not have percolated through the London Clay, it is likely that the silicification occurred in the late Palaeocene after deposition of the Upnor and Reading Formations, but before the Harwich or London Clay transgressions.

 Most of the sarsens also showed extensive fracture surfaces approximately perpendicular to their mammillated upper and lower surfaces. These joints may have formed by tectonic forces during the Alpine Orogeny, when already silicified sarsens had been deeply buried beneath younger deposits of Eocene age (London Clay, Claygate and Bagshot Beds). In a few of the sarsens, the mammillated surfaces were blackened. But no clear cause for this was agreed. Some thought the blackening was modern and had perhaps resulted from recent woodland fires or even bonfires, whereas others thought the surface might have been impregnated with iron or manganese deposited from solution during a late stage in the Palaeocene silicification process. Clearly sarsens and puddingstones continue to present numerous problems, which need to be tackled by modern analytical methods if their mode of formation and the exact environmental conditions at the time are to be clarified.

 Finally, we drove a short distance to Mill Wood, on the western side of Chafford Hundred, to see another section in unfossiliferous, decalcified fine sand of the Thanet Beds. This also provided a clear section in the Boyn Hill Gravels above the Thanet Beds. Thames View Hill, at the top of this quarry, afforded an excellent prospect across the Thames Valley towards north Kent, with a clear view westwards to the M25 bridge and yet further into central London.

 After thanking Di for a very interesting and stimulating day in an area that we originally felt was geologically unpromising, we left her to return the obsolete key to the visitor centre, and drove home to Hertfordshire.

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